The invention relates to an optical system for lantern slide projection, especially to a system for increasing brightness in projectors for the projection of stars in planetariums and similar devices.
From the book by Letsch, "Das Zeiss-Planetarium," Gustav Fischer Verlag Jena 1955, the off-print "Bild der Wissenschaft," Deutsche Verlagsanstalt Stuttgart 1977, and the "Jenaer Rundschau" (1967), issue No. 3, pages 177 to 1981 and (1968), No. 6, pages 345 to 349, it has been known in the planetarium industry to provide the projectors with hollow balls for the projection of fixed stars. A source of light assembled in a central position in each of the hollow balls provides all the projectors with light. Each projector is provided herein with a dia whose picture content contains small permeable fields in an absorbent material corresponding to the stars in the star field in question to be projected. These dias are illuminated by a source of light through associated lenses, the light traversing the openings projected by individual objectives onto the internal side of the dome.
Generally, all projections in which only a small portion of the light is used for image reproduction in view of the picture content of the original (as is the case in most projected objects in planetariums), have the disadvantage that the major portion of the light produced by the lamp is ultimately converted into undesirable heat. To improve brilliance and brightness of the projected images of the stars, it was necesary to install stronger light sources, which, in turn, resulted in increased heat generation.
Gas-discharge lamps have also been employed to increase brightness, which, however, make it necessary to provide all objectives with costly motor-driven diaphragms.
Individual projection systems have also been used in some planetariums, some having their own light source for projecting the brightest stars.
This invention, therefore, has the purpose of eliminating the disadvantages of the prior art, while increasing the portion of light in the projection.